Thank bees for orchids' diversity

作者：衡逝 发布时间：2019-03-07 02:13:03

By Michael Marshall Orchids owe their enormous variety to the bees and other insects that pollinate them. There are over 22,000 species in their family, the Orchidaceae. Most of them rely on animals to carry their pollen from one plant to another in order to reproduce. Tim Barraclough of Imperial College London and colleagues wondered if these pollinators were also the reason for orchids’ great variety. They studied 52 species of orchids belonging to the subtribe Coryciinae, which live in a small region of South Africa. These orchids attract pollinating insects with special oils: to get them, the insects delve deep into the flower. By looking at the orchids’ genes they worked out how the different species were related to each other and when they split from one another. At the same time they noted which insects pollinated which orchid, and how they went about it. Pairs of orchid species that had recently diverged tended to use different pollinator species from one another, and the few that shared the same pollinator placed their pollen on different parts of the insect’s body. For instance, the orchids Pterygodium pentherianum and Pterygodium schelpei live side by side, and place their pollen on the front legs and abdomen respectively of their pollinating bees (see picture). This ensures their pollen does not get mixed up, improving chances of successful reproduction. Barraclough’s team also looked at the mycorrhizae fungi that attach themselves to the orchids’ roots and live symbiotically with them, sometimes forming a vast underground network of fungal threads. Recently separated orchid species tended to use the same fungal species, suggesting that switching fungal partner was not an important factor in the formation of new species. Barraclough calls the findings “a fundamental insight into how so many new species can originate, and once they originate how they are able to coexist without exchanging genes”. “It’s a wonderfully carried-out study,” says Craig Barrett of Cornell University in Ithaca, New York. “I think their findings will apply in many groups of orchids.” However, he says that some orchids have radically different lifestyles from the ones Barraclough’s team studied, and the factors driving them to evolve may well be different. “A small percentage of orchids are self-pollinators,” he points out, so they do not need animal pollinators. Others have lost their leaves and live entirely by feeding off fungi. Journal reference: American Naturalist, DOI: 10.1086/657955 More on these topics: